Adjustable backlash system



1965 A. J. SUCHOCKI ADJUSTABLE BACKLASH SYSTEM 2 Sheets-Sheet 1 Filed Dec. 24, 1963 INVENTOR.

N 1965 A. J. sucHocKl ADJUSTABLE BACKLASH SYSTEM 2 Sheets-Sheet 2 Filed Dec. 24, 1963 .7 I I a k R0 mm .0 WM I #u% 9m M u M R n c 4 N w a United States Patent Ofiiice 3,216,272 Patented Nov. 9, 1965 3,216,272 ADJUSTABLE BACKLASH SYSTEM Anthony J. Suchocki, Clawson, Mich, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army Filed Dec. 24, 1963, Ser. No. 333,238 Claims. (Cl. 74-441) The present invention relates in general to improvement in screw drives and more particularly to improvements in elevating jacks for automatic weapons having a movable elevating gear threadedly mounted in a rotatable gearshaft.

In modern military vehicles machine guns or other automatic weapons are usually mounted in turrets or cupolas which can be rotated to traverse the weapon. To elevate, position and firmly hold these weapons on target hand-operated jacks are used. These jacks may incorporate an adjustable, elongated elevating gear or screw which can be connected to a trunnioned cradle that holds the gun in the cupola or turret. The elevating screw is extended or retracted by a rotating nut or gearshaft. By actuating the elevating gear, the gun cradle is rotated on the trunnions to raise and lower the weapon as necessary.

In previous elevating jacks, V-type screw threads were employed and the major diameter of the threads of the elevating gear and gearshaft were employed as the radial bearing surfaces. When the automatic weapons utilizing these jacks were fired, there was tipping or rocking of the gearshaft or nut gear on the elevating gear and the weapon would not be firmly held in its adjusted position. This instability resulted in the projectiles fired by the weapons being dispersed over a large area and not concentrated in a target zone.

This instability was largely due to the fact that it is extremely difiicult to machine and check the internal threads, particularly the major thread diameter of the gearshaft or nut gear, to close tolerance and smooth finish. Even when closely machined there remained residual looseness and backlash in the threaded connection and the elfectiveness of the weapon Was accordingly reduced.

It is therefore an object 'of this invention to provide an elevating jack for automatic weapons which will stabilize the weapon when being fired.

A further object of this invention is to provide a gun elevating jack to precisely train the gun on an intended target.

Another object of this invention is to provide a jack in which close tolerances between the threaded jack connections can be easily and economically maintained.

Another object of this invention is to provide an elevating jack which incorporates a vernier adjustment to compensate for manufacturing tolerances between the threads of the elevating nut and elevating gear.

Another object of this invention is to provide an elevating jack incorporating an adjustable means with vernier adjustment for eliminating backlash between the elevating gear and gearshaft.

The invention is fully disclosed by way of example in the following description and the accompanying drawing in which:

FIG. 1 is a diagrammatical side view showing the elevating jack installed in a cupola to rotate a gun cradle for adjusting gun inclination.

FIG. 2 is a side view of the elevating jack.

FIG. 3 is a cross sectional view of FIG. 1 taken along line 3-3 of FIG. 2.

FIG. 4 is a top view of the elevating gear used in FIGS. 2 and 3.

FIG. 5 is a diagrammatical view illustrating the threaded connection between the threaded elements of FIGS. 2 and 3.

FIG. 6 is an end view of the gearshaft taken along line 66 of FIG. 3.

Referring more particularly to the drawings wherein like reference characters refer to like parts, the gun elevating jack 1 has one end secured by bolt means 8 to rigid brackets 2 fastened to an upper interior portion of the cupola 12 and the other end secured by pivot bolt 10 to a gun cradle 4 rotatably mounted on trunnions 6 in the cupola. Mounted in the gun cradle 4 is a machine gun or other automatic weapon 14 which is elevated or lowered by the expansion or contraction of the jack to cause the rotation of cradle 4.

To provide for such gun motion, the gun elevating jack 1 has a hollow tubular housing 3 which has at one end a flat extension 5 to receive bracket 2. This extension has formed therein an opening in which a cylindrical bearing 7 is fitted for reception of a pin or bolt means 8 for rotatably fastening housing 3 to the cupola. A tubular, gearshaft 9 with internal square threads is rotatably mounted about its longitudinal axis on bearings 23 and 25 in housing 3. An elongated, cylindrical elevating gear 11 formed with external square threads 13 is threadedly connected to the gearshaft 9 as best shown by FIGS. 3 and 5. The outer end of the elevating gear is flattened at 15 and has formed therein a circular opening for reception of bearing 17.

Connector bolt 10 extends through bearing 17 and rotatably secures the elevating gear to a lower portion of the gun cradle 4 offset from the trunnions as illustrated in FIG. 1. A packing nut 19 is threadedly connected to a forward internal portion 21 of the housing 3 as best shown in FIG. 3 to hold the gearshaft in the housing. The opposite end of the gearshaft 9 is beveled and has a ring of gear teeth 29 formed therein which is concentric with the axis of rotation of the gearshaft. Also, mounted for rotation in the housing is a circular bevel gear 31 formed with teeth 33 completely around its circumference adapted to engage the teeth 29 of the gearshaft. As best seen from FIG. 3, the bevel gear 31 has an extension 35 which projects through the bifurcated end portion 37 of the elevating gear to prevent rotation thereof. Bevel gear 31 is rotatably mounted in housing 3 by bearing 36 fixed in the housing and by bearing 38 seated in a circular cover plate 40 removably secured to housing 3 by fasteners 43.

Elongated crank arm 39 is rigidly fastened by pin 41 to the bevel gear while a handle 42 is rotatably mounted to the crank arm by a pivot pin. On rotation of the crank arm 39 the bevel gear 31 will rotate and drive the gearshaft 9 around its horizontal axis. Since extension 35 extends between bifurcations in the elevating gear, that gear will not rotate but, due to the threaded connection between the gearshaft and elevating gear, will be driven longitudinally by the rotating gearshaft of the elevating gear. This longitudinal movement rotates the gun cradle 4 around pinion 6 to raise or lower the machine gun depending on direction of crank arm rotation.

Since great strength is required for transmission of power and motion to the gun and maximum stability is required to firmly hold the gun in position when being fired, cooperating square or modified square threads are utilized on the elevating gear and the gearshaft 9. As will be seen from FIGS. 3 and 5, these threads are practically perpendicular to the longitudinal axes of the elevating gear and the gearshaft and with their strong thread sections transmit power nearly parallel to these longitudinal axes.

To have a radially close threaded fit between the elevating gear and the gearshaft the minor diameter D of the gearshaft thread and the minor diameter d of the elevating gear thread are used as the radial bearing surfaces. These minor diameters are readily accessible and can be easily machined to close tolerance and smooth finish. This is possible since the minor diameter of the gearshaft is the internal diameter of that element. Due to the construction of the gearshaft, the major diameter is inaccessible and cannot be as easily machined or finished with the same close radial tolerance. By uitilizing the minor diameters d and D instead of the major diameters as the radial bearing surfaces and holding these minor diameters to close tolerance, the longitudinal axes of the gearshaft and elevating gear are maintained in coincidence and there will be no tendency of the gearshaft to rock or tip on the elevating gear when the gun 14 is fired. With the elimination of this rocking or tipping the accuracy of the machine gun is increased. In addition to increased gun accuracy, the use of the minor diameters as the radial bearing surfaces solves manufacturing problems and expense inherent in the use of the major thread diameters as radial bearing surfaces.

To compensate for mechanical wear between the threads of the elevating gear and gearshaft or to compensate initially for any large manufacturing tolerances in the thread sections, an adjustable internally threaded nut 47 is utilized as hereinafter described. As best shown by schematic FIG. 5, this nut has a square thread and is formed with a fiat face or shoulder 61 adapted to contact the flat inner face or shoulder 63 formed on the end of the gearshaft 9. As further best illustrated by FIG. 5, the square threads 67 on the gearshaft 9, which may be relieved as shown, are adapted to closely contact the outer face 65 of the elevating gear 13 while the thread of the nut 47 is adapted to closely contact the inner face 59 of the thread of the elevating gear. Thus, the nut 47 and gearshaft 9 carry loads in opposite directions.

If there is backlash or lost motion between the elevating gear and gearshaft the nut 47 can be rotated and advanced on the elevating gear until shoulders 61 and 63 are in close engagement and there is a tight thread fit between the thread sections to eliminate any lost motion. It is therefore apparent that nut 47 enables manufacture of the threads without the heretofore required close manufacturing tolerances in the sections of the thread or tooth thickness and eliminates the need for selective assembly of the elevating gear and the gearshaft.

A Vernier adjustment is provided between the nut and gearshaft to allow for incremental and controlled relative movement between the two elements. This can be accomplished for example by cutting an even number of equally spaced slots or grooves 51 in the cylindrical end of the gearshaft as shown in FIG. 6 While cutting an odd number of slots 53 in the outer periphery of the nut. For example, 15 slots may be cut into the nut while 16 slots may be cut into the gearshaft. Elongated locking key 49, adapted to be placed into any two aligned slots, prevents rotation of the nut and gearshaft with respect to each other. A semi-circular snap ring 55 is adapted to be positioned around the forward position of the gearshaft to securely hold the key in position in any two slots 5153 which are aligned in the adjustment.

The slot arrangement given as an example above will give 240 adjustments per revolution. If the lead on the thread of the elevating gear is .200 inch, the axial backlash can be controlled in increments of .200/240 or .00083 inch. It is therefore clear that when backlash or lost motion occurs the key can be removed and the nut advanced toward the elevating gear to contact surface 63 of gearshaft to effect a tighter thread contact or close fit between the threads of the elevating gear and the gearshaft and between the adjusting nut 47 and the gearshaft. Obviously, other slot relationships may be substituted for the one given as an example above.

With the present antibacklash adjustment the use of biasing springs has been avoided since the vibrations created by the firing machine gun would overcome such springs and there would be no effective backlash compensation.

It is therefore apparent that the device disclosed above enables the gun to be elevated and fired with a high degree of accuracy. The firepower of the gun will be concentrated in a small zone since the gun will be firmly held by the elevating jack. Furthermore, the present invention has disclosed an efiicient and accurate antibacklash device which is simple and economical in construction, easy to adjust and maintain, and adds materially to the accuracy of the weapon.

Although my invention has been described in connection with the elevation and depression of an automatic weapon, it is to be understood that it may be used in other environments where a tight threaded fit is desired.

Having described the invention what is claimed is:

1. A jack comprising a housing, a gearshaft rotatably mounted in said housing, an elongated gear threadedly mounted in said gearshaft, said gearshaft being rotatable relative to said gear, a nut threadedly mounted on said gear, said nut being adjustable on said gear relative to said gearshaft to permit a close threaded fit between said nut and gear and between said gearshaft and gear, said nut having a series of slots formed therein, said gearshaft having a series of slots formed therein near one end thereof, a key adapted to be positioned in selective slots in said nut and said gearshaft, means for retaining the key in the selected slots in said gearshaft and said nut.

2. The structure defined in claim 1 wherein the slots in said nut and gearshaft are arranged to provide a vernier adjustment between said nut and said gearshaft.

3. The structure defined in claim 1 wherein said nut and said gearshaft are formed with contact shoulders thereon, said shoulders when in contact with each other providing means to force said nut, said gearshaft and said gear into a close threaded fit.

4. An elevating jack comprising a housing, a gearshaft rototably mounted in said housing, said gearshaft being formed with a flat abutment shoulder thereon, an elongated elevating gear threadedly mounted in said gearshaft, said gearshaft being rotatable relative to said gear, a nut having an abutment shoulder threadedly mounted on said elevating gear adapted to contact the abutment shoulder on said gearshaft, said nut and gearshaft being formed with slots therein, key means being adapted to fit in selected aligned slots in said nut and gearshaft, said nut and gearshaft being adapted to provide a close threaded fit with said elevating gear when said abutment shoulder of said nut is brought into contact with the abutment shoulder of said gearshaft.

5. A jack for adjusting the elevation of a machine gun comprising a housing, a gearshaft rotatably mounted in said housing, said gearshaft being formed with an abutment shoulder thereon, elevating means formed with a thread including outer and inner facing helical surfaces, said elevating means being threadedly mounted in said gearshaft, said gearshaft being rotatable relative to said elevating means, a nut having an abutment shoulder threadedly mounted on said elevating means, the threads of said nut being adapted to contact the inner facing helical surfaces of said elevating means, the threads of said gearshaft being adapted to contact the outer facing helical surface of said elevating means, said nut and gearshaft having means to prevent relative movement therebetween when said abutment shoulder of said nut has been brought into contact with the abutment shoulder of said gearshaft.

6. A jack for adjusting the elevation of a gun comprising a threaded elongated gear, a rotatable gearshaft, said gearshaft having a threaded portion forming a first nut, a second nut threadedly mounted on said gear, said first and second nuts being relatively axially adjustable, the

threads of said first nut being adapted to contact the screw threads of said gear at one side thereof, the threads of said second nut being adapted to contact the screw threads of said gear at the opposite side thereof, said first and second nut including means for incrementally controlling axial backlash between said nuts and gear.

7. The structure defined in claim 6 wherein the threads of said elongated gear, first nut and second nut are square and wherein the minor diameters of the threads of said nuts and gear are the radial bearing surfaces of the connection between said elongated gear and said nuts.

8. The structure defined in claim 7 wherein said means is formed by an odd number of slots in the periphery of said first nut and an even number of slots in said second nut and a key adapted to fit into any two selectively aligned slots.

9. A jack for adjusting the elevation of a gun comprising a threaded elevating gear, said elevating gear being formed with a square thread, a rotatable gearshaft being formed with a threaded portion forming a first nut, said nut being formed with internal square threads, said elevating gear being threadedly mounted in said first nut, a second nut having an internal square thread threadedly mounted on said elevating gear, said first and second nuts being relatively axially adjustable on said elevating gear, said nuts and elevating gear being formed so that the minor diameter of the threads of the nuts and gearshaft form the radial bearing surface thereof, said first nut being load carrying in one direction, said second nut being load carrying in an opposite direction, said first nut and said second nut being formed with shoulders adapted to contact each other, said first nut being formed with a selected number of peripheral slots therein, said second nut being formed with a difierent selected number of peripheral slots therein, a key adapted to be positioned into aligned slots in the two nuts, a snap ring adapted to securely hold the key into any two selectively aligned slots.

10. A jack comprising a housing, a tubular gearshaft rotatably mounted in said housing, said gearshaft being formed with internal square threads, a elevating gear being formed with an external square thread thereon, said elevating gear being mounted in said gearshaft, means mounted in said housing for rotating said gearshaft and preventing rotation of said elevating gear, a nut being formed with internal square threads mounted on said elevating gear, said nut having a shoulder for contacting the end of said gearshaft, said gearshaft and nut being threadedly mounted on said elevating gear with the minor diameters of their respecitve threads forming radial hearing surfaces, said nut provided with a given number of peripheral slots therein, said gearshaft being provided with a different number of slots therein, a key adapted to be positioned in any two aligned slots, said slots in said gearshaft and said nut providing a vernier for gaging movement of said nut relative to said gearshaft.

References Cited by the Examiner UNITED STATES PATENTS 667,664 2/01 Ambrose 74441 998,905 7/11 Jaques 151-15 2,791,128 5/57 Geyer et a1. 74-441 2,945,387 7/6O Geyer 74-441 3,094,011 6/63 Bradley 74441 DON A. WAITE, Primary Examiner. 

1. A JACK COMPRISING A HOUSING, A GEARSHAFT ROTATABLY MOUNTED IN SAID HOUSING, AN ELONGATED GEAR THREADEDLY MOUNTED IN SAID GEARSHAFT, SAID GEARSHAFT BEING ROTATABLE RELATIVE TO SAID GEAR, A NUT THREADEDLY MOUNTED ON SAID GEAR, SAID NUT BEING ADJUSTABLE ON SAID GEAR RELATIVE TO SAID GEARSHAFT TO PERMIT A CLOSE THREADED FIT BETWEEN SAID NUT AND GEAR AND BETWEEN SAID GEARSHAFT AND GEAR, SAID NUT HAVING A SERIES OF SLOTS FORMED THEREIN, SAID GEARSHAFT HAVING A SERIES OF SLOTS FORMED THEREIN NEAR ONE END THEREOF, A KEY ADAPTED TO BE POSITIONED IN SELECTIVE SLOTS IN SAID NUT AND SAID GEARSHAFT, MEANS FOR RETAINING THE KEY IN THE SELECTED SLOTS IN SAID GEARSHAFT AND SAID NUT. 